1. Field of the Invention
The present invention relates to an X-ray imaging apparatus and, more particularly, to an X-ray imaging apparatus using a TV camera.
2. Description of the Related Art
In order to perform diagnosis, an X-ray imaging apparatus is used to radiate an X-ray to an object to be examined and to perform fluoroscopic observation of an X-ray image converted into an optical image by an image intensifier, or to photograph the X-ray image. In such an X-ray imaging apparatus, a fluoroscopic mode and a photographing mode are switched as required. However, in the fluoroscopic mode, weak X-ray energy beams are continuously radiated, and X-ray images are continuously picked up by a TV camera. Then, the images are displayed on a monitor and visually observed. On the contrary, in the photographing mode, an X-ray energy beam considerably stronger than that in the fluoroscopic mode is radiated, and an instantaneous X-ray image is photographed on a film. In this photographing mode, an optical image having a higher luminance by several tens of times than in the fluoroscopic mode is input to the TV camera, and a high luminance signal is supplied to a monitor. Therefore, in the conventional apparatus, an auto iris is provided at the front surface of the TV camera, and the quantity of light to be input to the TV camera is limited by the auto iris in the photographing mode.
As described above, in the conventional X-ray imaging apparatus, in order to set the quantity of light input to the TV camera to be a proper value, the auto iris, an auto iris control circuit, and the like are required. For this reason, an arrangement of a peripheral optical system of the TV lens and the TV camera is complicated. In addition, since the auto iris is a mechanical stop, reliability of the stop is problematic.